Explaining Moissanite’s Cut

January 1, 2004byGary Roskin

A new booklet, published by Charles & Colvard Ltd., the sole manufacturer and distributor of created moissanite jewels, claims that special cut proportions allow moissanite to exhibit “more brilliance, fire, and luster than any other jewels used in the creation of jewelry.” The booklet, titled CUT: Its Relevance and Importance As It Pertains to a Jewel’s Optical Physics, was written by Earl Hines, vice president of manufacturing for Charles and Colvard, and Kurt Nassau, Ph.D., author, research scientist, and gemstone expert.

Although moissanite’s hardness of 9.25 on the Mohs scale doesn’t match diamond’s 10, the authors claim that scientific measurements of luster, dispersion, and brilliance prove that moissanite (a.k.a. silicon carbide) outshines diamond. The key is in the cutting, which is designed to take advantage of moissanite’s refractive index, which is slightly higher than that of diamond.

Although diamond’s hardness allows it to take a better polish, enhancing light reflection and increasing luster, moissanite’s refractive index (2.65 vs. 2.42) allows less light to enter the stone, which means more light bounces off its surface, polish notwithstanding. Thus, moissanite reflects 20.4% of light vs. 17.2% for diamond.

Moissanite also exhibits more than twice as much dispersion (fire) as diamond (.104 vs. .044). As for brilliance, when both are cut to their own (not identical) ideal proportions, moissanite scores higher. Here’s why: Light within a gem can exit either through the top (brilliance) or through the pavilion (light leakage). Based on refractive index, every facet of every gem reflects light that approaches its surface at an angle greater than the critical angle. Light will be refracted out of the stone only if the light approaches the facet at an angle less than the critical angle. The critical angle cone of diamond is larger and accepts more light to leak out than does moissanite. Moissanite’s smaller critical angle cone allows more light to be reflected off the facet and up through the crown—if the stone is cut properly—showing up as greater brilliance.

All of which explains why moissanites are cut shallow. “Some of our retailers and distributors hold it in profile,” says Barbara Mooty, vice president, brand development and industry relations for Charles & Colvard. “It doesn’t have a diamond’s ideal cut,” and that confuses them, she says.

Every gem has its own unique angles that produce the ideal balance of brilliance and dispersion. For example, a 34.5° angled crown facet on a diamond is ideal for dispersion but on a moissanite will block light from escaping the stone. Thus, moissanite should not be cut to Tolkowsky proportions.